Space Glossary
Space words explained simply—from asteroids to space shuttles. Choose a letter or browse the page.
A
Asteroid
A large rock that travels around the Sun. Many asteroids lie between Mars and Jupiter. Scientists track them because a large asteroid hitting Earth could cause a disaster.
Asteroid Belt
The region between Mars and Jupiter where many rocky asteroids orbit the Sun. Some are as large as mountains.
Astronaut
A person trained to travel and work in space. The word is commonly used in the United States and several other countries.
Astronomy
The science of everything we see in the sky, including stars, planets, comets and galaxies. Astronomers use telescopes and images to learn how space works.
Astrophysics
A branch of astronomy that explains why things happen in space: why stars shine, why planets orbit and how black holes form.
Atmosphere
The layer of gases around a planet. Earth’s atmosphere gives us air to breathe and protects us from the cold of space and harmful sunlight.
Aurora
Colourful light in the sky caused when particles from the solar wind meet a planet’s atmosphere. Auroras are most common near the poles.
B
Big Bang
The name scientists give to the beginning of the Universe, when space began expanding extremely quickly from a tiny, hot state nearly 14 billion years ago.
Black Hole
A region where gravity is so strong that even light cannot escape. Many black holes form from the remains of massive stars.
C
Comet
A ball of ice, dust and rock that orbits the Sun. As it approaches the Sun, it warms up and develops a bright tail.
Constellation
A recognised pattern of stars as seen from Earth, such as Ursa Major. The stars in a constellation may actually be very far apart.
Cosmonaut
The word traditionally used for an astronaut trained in Russia and several other countries. Cosmonauts and astronauts do the same kind of work.
Crater
A round hollow on the surface of a planet or moon, often formed when a meteorite strikes. The Moon and Mercury are covered in craters.
D
Dwarf Planet
A round object that orbits the Sun but is not classed as a full planet. Pluto is the best-known example.
G
Galaxy
A vast city of stars held together by gravity. Our galaxy is the Milky Way, and it contains more than one hundred billion stars.
Gas Giant
A huge planet made mostly of gases rather than solid rock. Jupiter, Saturn, Uranus and Neptune are the gas and ice giants of our Solar System.
Gravity
The force that pulls objects towards one another. It keeps us on Earth and keeps planets travelling around the Sun.
H
Horoscope
A chart that claims the positions of stars and planets are linked to a person’s character or future. Astronomy treats horoscopes as tradition, not science.
I
ISS (International Space Station)
A huge laboratory that orbits Earth. Astronauts from different countries live there, perform experiments and observe our planet.
K
Kármán Line
An imaginary boundary 100 kilometres above Earth that is widely used to mark where the atmosphere ends and outer space begins.
Kuiper Belt
A distant region beyond Neptune filled with icy worlds and dwarf planets. Pluto is part of the Kuiper Belt.
L
Laniakea
The enormous supercluster of galaxies that includes the Milky Way. Its name means “immense heaven” in Hawaiian.
Launch Vehicle
A large multi-stage rocket that carries satellites, probes or spacecraft into orbit. Empty stages separate during flight so the rocket becomes lighter.
Light-Year
The distance light travels in one year, almost 10 trillion kilometres. Astronomers use light-years because distances between stars are so vast.
M
Magnetic Field
An invisible shield around Earth that deflects much of the solar wind and many dangerous particles from space.
Mars Rover
A robotic vehicle that drives across Mars, takes photographs, drills into rocks and searches for signs of water and past life.
Meteor
The bright streak we call a shooting star. It appears when a small space rock burns up in Earth’s atmosphere.
Meteorite
A piece of space rock that survives its journey through the atmosphere and reaches the ground.
Meteoroid
A small rock or piece of metal travelling through space. In the atmosphere it becomes a meteor; if it reaches the ground, it is a meteorite.
Milky Way
Our home galaxy, containing more than one hundred billion stars. From Earth, part of it looks like a pale, misty band across the night sky.
N
Nebula
A vast cloud of gas and dust in space. Some nebulae are places where new stars are born, and many appear bright and colourful.
Neutron Star
An incredibly dense object left after a massive star explodes. A teaspoon of neutron-star material would weigh billions of tonnes.
Northern Lights
Another name for the aurora borealis: green, red, blue or violet light produced when the solar wind interacts with Earth’s atmosphere in the north.
O
Observatory
A building or facility equipped with telescopes and instruments for studying stars, planets and other objects in space.
Oort Cloud
A vast, distant shell of icy objects surrounding the Solar System. Reaching it with today’s spacecraft would take tens of thousands of years.
Orbit
The curved path one object follows around another. The Moon orbits Earth, and Earth orbits the Sun.
P
Planet
A large, nearly round object that travels around a star. Eight planets orbit the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Planetarium
A theatre with a domed screen that shows the night sky. Visitors can watch stars and planets move and take a virtual journey through space.
Planetoid
A small object orbiting the Sun that is too small to be a planet. The word is often used for minor planets and sometimes dwarf planets.
R
Radiation
Energy that travels as waves or particles. Some kinds of space radiation can harm living things and electronics; Earth’s atmosphere and magnetic field protect us from much of it.
Rocket
A powerful vehicle that burns fuel and pushes exhaust downwards, producing the force needed to rise against Earth’s gravity.
S
Satellite
An object that orbits a planet or another body. The Moon is Earth’s natural satellite; people have also built thousands of artificial satellites.
Solar Radiation
Energy and fast particles released by the Sun. Earth’s atmosphere protects us, while astronauts may need extra shielding during strong solar storms.
Solar System
The Sun and everything that orbits it: eight planets, their moons, dwarf planets, asteroids, comets, dust and ice.
Solar Wind
A continuous stream of charged particles flowing from the Sun. It can affect satellites and astronauts and also helps create auroras.
Space Debris
Old satellites, rocket fragments and other human-made objects left orbiting Earth. Scientists are working on ways to reduce and remove it.
Space Probe
An uncrewed robotic spacecraft sent to photograph and study distant worlds. Voyager 1 and Voyager 2 are famous examples.
Space Shuttle
A reusable spacecraft that launched like a rocket and landed like an aircraft. NASA’s Space Shuttles flew from 1981 to 2011.
Space Station
A large home and laboratory in orbit where astronauts live, work and carry out experiments. The International Space Station is the best-known example.
Spacecraft
A vehicle designed for space travel, such as a crew capsule, shuttle, probe or space station module.
Spacesuit
A protective suit that provides air and shields an astronaut from vacuum, extreme temperatures and some radiation during a spacewalk.
Star
A gigantic glowing ball of hot gas. Powerful reactions inside it release light and heat. The Sun is the closest star to Earth.
Sun
The star closest to Earth. Its light and heat make life on our planet possible.
Supernova
The enormous explosion of a massive star at the end of its life. It can briefly shine brighter than an entire galaxy and may leave behind a neutron star or black hole.
T
Taikonaut
A commonly used English term for a Chinese astronaut, derived from the Chinese word for space.
Telescope
An instrument that gathers light or other signals so we can study distant stars, planets and galaxies.
U
Universe
Everything that exists: all stars, planets, galaxies, space and even us.
W
Weightlessness
The condition in which people and objects appear to have no weight and float freely. Astronauts eat, sleep and work this way in orbit.
White Dwarf
The small, very dense remnant left when a star like the Sun grows old and stops producing energy. Our Sun will become one, but not for a very long time.